To improve emissions, vehicles, such as, for example, vehicles having diesel engines, may be equipped with particulate filters. For controlling such exhaust-gas treatment systems and/or for monitoring the condition of such exhaust-gas treatment systems, a variable may be evaluated which characterizes the flow resistance of the exhaust-gas treatment system or of individual components such as, for example, the particulate filter. The monitoring of the filter load in the case of particulate filters and the regeneration monitoring may be performed using pressure sensors, since the pressure drop through the filter may permit conclusions about the soot mass collected in the filter. The differential pressure to be measured through the filter may also be a function of the volumetric exhaust-gas flow.
In passenger-car engines having exhaust-gas recirculation, an air-mass sensor may be available whose measuring signal may also be used for determining the volumetric exhaust-gas flow. Should this sensor be dispensed with, or if a system exists without an exhaust-gas mass sensor, the volumetric exhaust-gas flow may not be readily determined, since this variable may not be measured directly, or doing so may cause undesirable expense.